The invention relates to an installation for producing at least hydrogen, this installation comprising at least:                a purification unit for purifying a hydrogen-rich synthesis gas and for producing hydrogen and a waste gas,        a first line (5; 105) for conveying the synthesis gas to the purification unit,        a second line (9: 109) for conveying the waste gas from the purification unit to burners, and        a buffer tank (14) placed in the second line.        
The invention also relates to a method to be employed when operating this installation, following an unscheduled shutdown of the purification unit.
Furthermore, the invention relates to a method for starting up certain sorts of installations of the aforementioned type and to a method for decreasing the hydrogen yield produced by same.
In an installation of the aforementioned type, the purification unit produces a waste gas which is recovered in order to be burned in the burners, to which the supply is interrupted during an unscheduled shutdown of this purification unit, which is disadvantageous.
In particular, this installation may be equipped with a methane reforming unit, this reforming unit being heated and provided for the purpose with burners in which the waste gas is burned. In such a configuration, an accidental shutdown of the purification unit often results in the shutdown of the reforming unit. This is a drawback, and is especially serious because the time required to restart this reforming unit amounts to tens of hours, all very costly. Furthermore, even in cases where the reforming unit is successfully kept in operation, it can only return to steady state conditions after several hours.
In consequence, numerous efforts have been made to improve the reliability of the purification units employed. However, these purification units still tend to stop accidentally.
The object of the invention, which aims in particular to correct the aforementioned drawback, is therefore to improve the operation and/or profitability of an installation of the aforementioned type.